I have been designing and prototyping a small pressure regulator to handle CO2 from standard small gas cartridges. The regulator is made of GF nylon 6/6 and is currently of the balance piston style. I am looking to regulate the 850 psi cartridge pressure to values between 5 and 40 psi. I seem to be having inconsistent results. I will get it to regulate quite well through several cartridges and then suddenly it becomes erratic. I have recently printed a housing from a translucent material which now allows me to get an idea of what is happening internally. What I have noticed is that when the regulator becomes erratic (returning to a pressure higher than it was set at or continually climbing) that I will see CO2 ice (dry ice) appearing on the regulated side of the balance piston (I know it is dry ice as I have removed some and examined it). This suggests that the high pressure valve (for which i am using a 5.5 mm stainless ball seated on a 90D urethane oring) is open or leaking past the oring seal. Questions: Why does it work fine for a number of exhaust and re-pressurize cycles and then become erratic? Is the dry ice forming because the ball is off the seat thus allowing a constant flow of gas?
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